It is known to use a laser beam to sever hair as an alternative to an arrangement of mechanical cutting blades. Hair exposed to a laser beam will absorb energy from the laser beam and the hair will either be severed by vaporisation or by laser induced optical breakdown and a resulting shockwave. A laser beam requires no moving parts and so the problem of cutting elements becoming worn or blunt is eliminated. Moreover, use of a laser beam to sever hair avoids skin irritation caused by the sharp edges of mechanical blades contacting the skin. It is known from WO1992/16,338 and U.S. Pat. No. 5,993,440 to provide a device including a laser diode and reflective elements that direct a laser beam across a cutting zone so that the beam is substantially parallel to and spaced from the surface of the user's skin during use. In this way, as the device is moved across the skin, hairs that enter the cutting zone are exposed to the laser beam and severed at the point of interaction between the laser beam and the hair.
Shaving performance is typically measured by two criteria—closeness of shave and irritation of the skin. The cutting height is the distance between the surface of the skin and the point at which hairs are cut. A good performing shaver should minimise the cutting height and therefore minimise the remaining hair length by cutting the hairs as close as possible to the skin. However, positioning a laser beam close to the skin may cause skin irritation if heat and energy from the laser is incident on the skin. It is therefore necessary to protect the skin from a laser beam to avoid causing damage or irritation to the skin.
It is known that sensations and potential side-effects due to hair removal using a laser beam, for example skin irritation, may vary from user to user depending on skin type, sun exposure, and between different ethnic groups.